a) Field of the Invention
The invention is directed to a microscope objective with axially adjustable correction mounts in which lenses or lens groups are arranged, particularly for live cell imaging and for cell culture and tissue culture research. The invention is applicable in microscope objectives in connection with different cover slips and/or different immersion liquids and/or at different work temperatures.
b) Description of the Related Art
With these kinds of axial adjustments of optical elements in objectives, different kinds of corrections can be carried out in order to enable microscopic examinations under various conditions with high quality and high lateral magnifications.
In microscope objectives, the axial adjustment of optical elements arranged in correction mounts in relation to stationary optical elements can be realized in different ways.
DE 38 12 745 C2 describes a microscope objective with an aperture of at least 0.5 and a device for adjusting to different cover slip thicknesses in which a second lens group is arranged so as to be linearly displaceable between a stationary first lens group and a stationary third lens group, an additional lens group being axially displaceable in the opposite direction relative to this second lens group. The movement strokes of these displaceable lens groups can differ. An individual actuating ring is provided for realizing the displacements of the corresponding lens groups. In this objective, the device for adjusting to different cover slip thicknesses is coupled with a device for refocusing the entire objective. The lens groups are displaced linearly in the course of the adjusting movement. This can be achieved, for example, by means of threads of different pitches or by means of cams which engage in corresponding grooves with a constant but different pitch in a rotatable intermediate ring of the lens mount.
Further, EP 0 660 942 B1 discloses a microscope objective with at least one correction mount in which the correction mount is axially displaceable and is rotatable around the optical axis of the objective. A pin which is movable on a cam groove of a mount support and which is fixedly connected at one end to the correction mount and engages at the other end in a rotatable ring is provided for axial displacement and simultaneous radial rotation of the mount. Two axially displaceable and simultaneously rotatable correction mounts are provided in an objective disclosed in this reference.
DE 199 47 378 A1 describes an adjusting mechanism for an objective which is provided with an axially movable optical element that is connected to the main mount, or barrel, by a sliding mount. A first linear drive is connected by actuating members to a second linear drive which generates the linear movement along the optical axis. The second linear drive is connected to the sliding mount.
In order to ensure that the parts can move relative to one another without play in known objectives of the kind mentioned above, a uniform pressure is exerted on the mechanical structural component parts by springs or spring elements. Due to the large number of moving parts and the resulting frictional resistances and weight forces, the required spring force is usually so large that it is scarcely possible to use a conventional helical spring. A helical spring of this kind cannot be integrated within the limited space of a microscope objective. Movability of the structural component parts that is as unrestricted as possible is another criterion for the design of the spring. Some of the structural component parts in the microscope objective are rotated when correcting for different cover slips. In so doing, an individual helical spring is subjected to twisting stress which has a negative impact on the movability of the rotatable structural component parts.
DE 198 04 470 C1 discloses a microscope objective with a plurality of lens group mounts, one of which is formed as a correction mount for adapting to different cover slip thicknesses and is displaceable axially along the optical axis of the objective for changing position relative to stationary lens mounts. The axial displacement of the correction mount is carried out by means of a guide pin running on cam rings by actuating a knurled ring that is rotatable around the optical axis. To prevent tilting of the correction mount and to ensure the most uniform possible spring force over a large adjusting range, this solution provides a plurality of radially distributed pressure springs. Sleeves are arranged around the pressure springs for the purpose of free axial movement. It is disadvantageous that every pressure spring is integrated in a sleeve for guiding in order to prevent the springs from buckling. This sleeve takes up extra space in the microscope objective. Nevertheless, since the pressure springs are not completely guided in the sleeve in the interest of ensuring the spring path, buckling can occur in the exposed area. In this construction, none of the contact surfaces of the individual springs may be subjected to a rotating movement because this would result in a buckling of the springs.